J/ApJ/910/46 Galactic anticenter substructure stars from LAMOST (Li+, 2021) ================================================================================ Exploring the Galactic anticenter substructure with LAMOST and Gaia DR2. Li J., Xue X.-X., Liu C., Zhang B., Rix H.-W., Carlin J.L., Yang C., Mendez R.A., Zhong J., Tian H., Zhang L., Xu Y., Wu Y., Zhao G., Chang R. =2021ApJ...910...46L ================================================================================ ADC_Keywords: Milky Way; Stars, giant; Stars, K-type; Stars, M-type; Proper motions; Radial velocities; Abundances; Surveys; Optical Keywords: Milky Way stellar halo ; Milky Way disk ; Stellar kinematics ; Chemical abundances Abstract: We characterize the kinematic and chemical properties of 589 Galactic anticenter substructure stars (GASS) with K/M giants in integrals-of-motion space. These stars likely include members of previously identified substructures such as Monoceros, A13, and the Triangulum-Andromeda cloud. We show that these stars are in nearly circular orbits on both sides of the Galactic plane. We can see a velocity (VZ) gradient along Y-axis especially for the south GASS members. Our GASS members have similar energy and angular momentum distributions to thin-disk stars. Their location in [{alpha}/M] versus [M/H] space is more metal-poor than typical thin-disk stars, with [{alpha}/M] lower than that of the thick disk. We infer that our GASS members are part of the outer metal-poor disk stars and that the outer disk extends to 30 kpc. Considering the distance range and {alpha}-abundance features, GASS could be formed after the thick disk was formed due to the molecular cloud density decreasing in the outer disk where the star-formation rate might be less efficient compared to the inner disk. Description: The data used in this work consist of spectroscopically identified K and M giants from LAMOST Data Release 5 (DR5). The LAMOST Telescope is a 4m Schmidt telescope at Xinglong Observing Station which provide low-resolution (R~1800) optical spectra. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 286 589 Parameters of Galactic anticenter substructure stars (GASS) table2.dat 298 589 Orbital parameters of GASS stars -------------------------------------------------------------------------------- See also: III/46 : Ap and Am Stars (Bertaud+ 1974; Bidelman+ 1973) I/345 : Gaia DR2 (Gaia Collaboration, 2018) I/347 : Distances to 1.33 billion stars in Gaia DR2 (Bailer-Jones+, 2018) III/284 : APOGEE-2 data from DR16 (Johnsson+, 2020) J/AJ/100/1191 : Giants DDO photometry (Morrison+, 1990) J/ApJS/96/175 : Kinematics of Metal-Poor Stars. I. (Beers+ 1995) J/AJ/115/168 : Kinematics of red giant and RR Lyrae stars (Chiba+ 1998) J/AJ/119/2866 : Proper motions of metal-poor stars (Beers+, 2000) J/ApJ/588/824 : Velocities of blue stars near (l,b)=(198,-27) (Yanny+, 2003) J/A+A/410/527 : Abundances in the Galactic disk (Bensby+, 2003) J/A+A/493/71 : UBV photometry of Shorlin 1 (Carraro+, 2009) J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012) J/A+A/562/A71 : Abundances of solar neighbourhood dwarfs (Bensby+, 2014) J/ApJ/784/170 : The SEGUE K giant survey. II. Distances (Xue+, 2014) J/ApJ/788/180 : Very metal-poor stars in the Milky Way's halo (Carollo+, 2014) J/ApJ/794/58 : Metal-poor stars in the thick disk of the Galaxy (Beers+, 2014) J/ApJ/823/59 : WISE and 2MASS photometry of M giant stars (Li+, 2016) J/ApJS/226/1 : Carbon stars from LAMOST DR2 data (Ji+, 2016) J/ApJ/854/47 : RRab stars of Monoceros & A13 overdensities (Sheffield+, 2018) J/ApJS/234/31 : Carbon stars from LAMOST using machine learning (Li+, 2018) J/ApJ/859/L8 : Properties of TriAnd stars (Hayes+, 2018) J/ApJ/880/65 : LAMOST K giants in Galactic halo substructures (Yang+, 2019) J/ApJS/244/8 : M-type stars in LAMOST DR5 (Zhong+, 2019) J/ApJ/886/154 : Sgr stream K- & M-giants and BHB stars (Yang+, 2019) J/ApJS/246/9 : Stellar parameters of LAMOST stars using SLAM (Zhang+, 2020) Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 9 I9 --- LAMOST [216068/584303141] LAMOST unique identifier 11- 29 I19 --- Gaia Gaia DR2 solution identifier 31- 39 A9 --- Type Source type (1) 41- 51 F11.7 deg RAdeg Right Ascension in decimal degrees (J2000) 53- 62 F10.7 deg DEdeg Declination in decimal degrees (J2000) 64- 82 F19.16 kpc Dist [6/32.5] Distance (2) 84-102 F19.17 kpc e_Dist [0.3/8] Uncertainty in Dist 104-117 F14.9 km/s HRV [-199.1/152.4] Heliocentric radial velocity 119-129 F11.8 km/s e_HRV [0/56] Uncertainty in HRV 131-152 F22.19 mas/yr pmRA [-2.5/0.9] Gaia DR2 proper motion along RA 154-173 F20.18 mas/yr e_pmRA [0.02/0.8] Uncertainty in pmRA 175-195 F21.18 mas/yr pmDE [-4.1/0.6] Gaia DR2 proper motion along DE 197-216 F20.18 mas/yr e_pmDE [0.02/0.6] Uncertainty in pmDE 218-239 F22.19 [Sun] [M/H] [-5.3/1.7] Metallicity (3) 241-251 F11.9 [Sun] e_[M/H] [0.029/0.5] Uncertainty in [M/H] 253-274 E22.10 [Sun] [a/M] [-0.32/3.2] Log {alpha}-elements to metals abundance ratio (3) 276-286 F11.9 [Sun] e_[a/M] [0.019/0.2] Uncertainty in [a/M] -------------------------------------------------------------------------------- Note (1): Type as follows: LAMOST KG = LAMOST DR5 K giant (309 occurrences) LAMOST MG = LAMOST DR5 M giant (280 occurrences) Note (2): We recalibrated the distances of K and M giants by the Gaia DR2 parallax. See Section 2.1. Note (3): From Zhang et al. (2020, J/ApJS/246/9); see Section 2.1. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 9 I9 --- LAMOST [216068/584303141] LAMOST unique identifier 11- 28 F18.15 --- e [11.6/43] Eccentricity 30- 50 F21.17 --- e_e [0.2/409] Uncertainty in e 52- 71 F20.18 kpc a [0.058/0.55] Semi-major axis 73- 93 F21.19 kpc e_a [0.0039/0.2] Uncertainty in a 95-115 F21.17 deg lOrb Galactic longitude of orbital pole 117-136 F20.16 deg e_lOrb [0.5/175] Uncertainty in lOrb 138-155 F18.14 deg bOrb [144/175] Galactic latitude of orbital pole 157-176 F20.17 deg e_bOrb [0.17/14] Uncertainty in bOrb 178-197 F20.16 deg lApo Galactic longitude of apocenter (1) 199-218 F20.16 deg e_lApo [4.1/174] Uncertainty in lApo 220-238 F19.12 km2/s2 E [-96052/-53139] Energy 240-258 F19.13 km2/s2 e_E [620/16806] Uncertainty in E 260-277 F18.13 km/s/kpc L [2362/7054] Angular momentum 279-298 F20.15 km/s/kpc e_L [38/2275] Uncertainty in L -------------------------------------------------------------------------------- Note (1): i.e. the angle between apocenter and the projection of x-axis on the orbital plane). Please note that lApo changes with periods, but keeps constant within one period, which can be used to distinguish stars in the same stream but involving in our Galaxy in different epochs (e.g. Sgr leading and trailing arms). -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Prepared by [AAS], Emmanuelle Perret [CDS] 12-Aug-2022